Enhancements in sheet processing and lead formation

ABSTRACT

A connection component for making microelectronic assemblies includes a dielectric structural layer having a first surface and a plurality of conductive leads having first and second ends overlying the first surface of the dielectric structural layer. An adhesive is provided between the second ends of the leads and the dielectric structural layer such that the adhesive forms connections between the second ends of the leads and the structural layer. The formed connections have areas smaller than the areas of the second ends. The second ends of the leads are releasably attached to the structural layer by the connections. Thus, the second ends of the leads may be engaged with features on a microelectronic device and the microelectronic elements may be moved away from the structural layer so as to bend the second ends of the leads away from the structural layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims benefit of United States ProvisionalPatent Application No. 60/131,322, filed Apr. 27, 1999, the disclosureof which is hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

As described in co-pending, commonly assigned U.S. patent applicationSer. Nos. 09/173,797 and 09/174,074 both filed Oct. 16, 1998, thedisclosures of which are incorporated by reference herein, sheet-likeelements for use in microelectronic devices can be fabricated and/orassembled while the sheet-like element is held under tension and aframe. For example, a sheet for forming microelectronic connectioncomponents may incorporate dielectric layer such as a polyimide sheet.The polyimide sheet may be attached to a frame using an adhesive. Theframe may be made of a relatively rigid material having a known,predictable coefficient of thermal expansion such as glass, quartz, ormolybdenum. While the sheet is held in tension, features such asmetallic leads, contacts and the like can be formed on the surfaces ofthe sheet by additive processes such as electroplating and/orsubtractive processes such as etching. The sheet, with the featuresthereon, can be aligned with a microelectronic element such as asemiconductor wafer or an assemblage of discrete chips while the sheetis maintained on the frame. Because the sheet is maintained in tensionby the frame, and because the frame has known, predictable thermalexpansion properties, all of the features on the sheet can be maintainedat precise locations relative to one another. The features on the sheetcan be precisely aligned with features on the microelectronic element.

As disclosed in certain embodiments of U.S. Pat. No. 5,518,964, thedisclosure of which is also incorporated by reference herein, leads canbe fabricated on other supports such as dielectric bodies orsemiconductor elements so that each lead has one end permanentlyanchored to the support and another end releasably attached to thesupport. The support, with the leads thereon, can be engaged with amicroelectronic element so that the second ends of the leads areconnected to contacts on the microelectronic element, whereupon thesupport is moved away from the microelectronic element to bend theleads. During this process, the releasable attachments to the supportare detached.

As described in certain embodiments of co-pending, commonly assignedU.S. patent application Ser. No. 09/020,750 filed Feb. 9, 1998 and Ser.No. 09/195,371 filed Nov. 18, 1998, the disclosures of which are herebyincorporated by reference herein, a releasable lead structure can bemade by providing a lead such as a metallic lead overlying a surface ofa dielectric layer and exposing the surface, with the leads thereon, toan etchant such as an oxidizing plasma which attacks the dielectric butwhich does not substantially attack the material of the lead. Theetchant removes the dielectric in areas not covered by the leads. Also,the etchant begins to remove material beneath the leads, starting at theedges of the leads and progressing inwardly from the edges of the leadstoward the center. The etching process is stopped before the dielectrichas been completely removed beneath all portions of the lead. Thisleaves the lead connected to the dielectric layer by a relatively smallconnecting element having an area smaller than the area in thehorizontal plane of the lead. The process can be used to provide suchsmall connecting elements as releasable connections at the second endsof the leads in structures such as those taught in the '964 patent.

The present invention provides certain enhancements to these processes.

SUMMARY OF THE INVENTION

One aspect of the invention provides a connection component for makingmicroelectronic assemblies. The apparatus according to this aspect ofthe present invention preferably includes a structural layer having afirst surface, a plurality of conductive leads each having a first endand a second end overlying the first surface of the dielectricstructural layer, the first ends of the leads being permanentlyconnected to the structural layer. Preferably, an adhesive is disposedbetween the second ends of the leads and the structural layer to formconnections between the second ends of the leads and the structurallayer. The connections desirably have areas smaller than the areas ofthe second ends, and the second ends of the leads may be releasablyattached to the structural layer by the connections. Connectioncomponents according to this aspect of the invention can be used in amanner similar to the components of the aforementioned patents andapplications. The use of the adhesive layer facilitates fabrication ofthe component.

The adhesive may extend between the first ends of the leads and thestructural layer and forms anchors having areas larger than the areas ofthe second ends. The structural layer can include either a dielectriclayer juxtaposed with the adhesive or a metallic layer. The componentpreferably further includes a frame overlying portions of the structurallayer, the adhesive retaining the structural layer in engagement withthe frame, the frame holding the structural layer in tension. Hereagain, use of the same adhesive layer to hold the leads and framefacilitates fabrication of the component.

A further aspect of the present invention provides a in-processcomponent for making electronic connection components. The in-processcomponent preferably includes a frame having structure defining anaperture and a sheetlike composite element including a structural layerhaving oppositely-directed first and second surfaces. A first adhesivelayer desirably overlies the first surface of the structural layer. Thecomposite element preferably includes peripheral portions overlying thestructure of the frame and a central portion aligned with the aperture.Desirably, the adhesive layer extends into the peripheral portions andsecures the structural layer to the frame. The adhesive layer alsoextends into the central portion of the composite element. Thestructural layer may include a dielectric layer. Desirably, thecomponent further includes a metallic layer overlying the centralportion of the composite element and secured to the structural layer bythe adhesive layer. The in-process component may further include asecond adhesive layer overlying the second surface of the structurallayer, and may also include a metal layer overlying the second adhesivelayer. The in-process component can be used, for example, to makeconnection components as discussed above.

Yet another aspect of the present invention provides a method of makinga connection component with releasable leads. The method according tothis aspect of the present invention preferably includes the steps ofproviding a structural layer and elongated leads having first and secondends overlying a first surface of the structural layer. Desirably, anadhesive is disposed between the structural layer and the second ends ofthe leads. The adhesive is preferably etched with an etchant whichattacks the adhesive but does not substantially attack the leads so asto partially remove the adhesive beneath the second ends of the leads tothereby form connections having areas smaller than the areas of thesecond ends of the leads. Preferably, the adhesive is provided as alayer on the structural layer. A layer of metal is desirably providedoverlying the structural layer and the layer of metal is selectivelyetched to form leads. An electrically conductive seed layer ispreferably provided on the layer of adhesive and the leads areselectively plated onto the seed layer. The seed layer is then desirablyremoved except in the regions beneath the leads. A frame may also beprovided to define an aperture such that the structural layer extendsacross the aperture, and the adhesive layer extends between thestructural layer and the frame. The structural layer may then be securedto the frame.

These and other objects, features and advantages of the presentinvention will be more readily apparent from the detailed description ofthe preferred embodiments set forth below, taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic sectional view, on an enlarged scale of aconnection component in accordance with one embodiment of the invention.

FIG. 2 is a view similar to FIG. 1 but depicting the component in alater stage of the process.

FIG. 3 is a fragmentary, diagrammatic plan view depicting a portion ofthe component illustrated in FIG. 2.

FIG. 4 is a fragmentary, diagrammatic sectional view taken along line4—4 in FIG. 3.

FIG. 5 is a fragmentary, diagrammatic sectional view depicting acomponent according to a further embodiment of the invention.

FIG. 6 is a view similar to FIG. 5 but depicting the component during alater stage of the process.

FIG. 7 is a view similar to FIG. 6 but depicting the component during alater stage of the process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A process in accordance with one embodiment of the invention begins witha starting structure including a structural layer 10 having a firstadhesive layer 12 on a first surface and a second adhesive layer 14 onthe oppositely-directed second surface of structural layer 10. Thestructural layer 10 is depicted in FIG. 1 as including only a singlelayer of a dielectric such as a polyimide. Such a single layer structuremay be used in practice. However, more complex structures incorporatingmultiple dielectric layers and/or also incorporating internal conductivefeatures such as vias, traces, and electrically conductive potentialplanes may also be used. The starting structure may be a structure ofthe type commonly referred to as a “bond ply.”

The starting structure is bonded to a frame 16 having a structure 18defining a central aperture 20. As further described in theaforementioned '797 and '074 applications, the frame 18 may be agenerally a ring-like structure surrounding the aperture 20 on allsides. The first surface of structural layer 10 and first adhesive layer12 faces toward the frame, whereas the second surface of structurallayer 10 and the second adhesive layer 14 face away from the frame.Peripheral portions 21 of the structural layer are aligned with theframe, whereas a central portion 23 of the structural layer is alignedwith aperture 20. Heat and pressure may be applied during the bondingstep so as to activate the adhesive in a layer 12. Structural layer 10desirably is maintained under tension during the bonding process. Forexample, edge portions of the structural layer (not shown) may be pulledoutwardly during the bonding process. In the typical case where thestructural layer 10 has a coefficient of thermal expansion (“CTE”)greater than the CTE of the frame structure, the bonding operation isperformed at a relatively high temperature so that upon cooling to othertemperatures employed in subsequent processing, differential thermalexpansion and contraction can maintain tension in structural layer 10.

After the structural layer has been secured to the frame by adhesivelayer 12, a first metallic layer 22 and a second metallic layer 24 areformed on the first and second adhesive layers 12 and 14, respectively.Thus, layer 22 overlies the first surface of the structural layer 10,whereas layer 24 overlies the second surface of the structural layer.The metallic layers may be formed, for example, by depositing a “tiecoat” or adhesion promoting layer, such as a seed layer, formed from amaterial such as nickel using a sputtering process and then depositingadditional metal to form the layer by electroplating or electrolessplating. Typically, the metal which forms the layer may be copper, gold,or alloy containing one or both of these metals.

The additional metal used to form the layers by electroplating orelectroless plating can be deposited selectively onto the “tie coat” oradhesion promotion layer.

In an alternative, the metal layers may be applied to the startingstructure before the frame, or preferably, simultaneously with theframe. For example, layers 22 and 24 can be bonded to the structurallayer using the same adhesive layers 12 and 14 at the same time as theframe is bonded to the structural layer. Also, one of the metal layersmay be formed by a plating process as discussed above whereas the othermay be provided as a pre-laminated structure. For example, a continuousmetal layer 24 may cover the bottom surface of the starting structureprior to joining the starting structure with the frame, whereas layer 22may be formed in place after the frame has been attached.

After the metal layers have been formed, they are treated to define aset of individual metallic features overlying the surfaces of structurallayer 10. When a layer is formed selectively, the adhesion promotionlayer and adhesive layer are removed, except in regions beneath theselectively formed layer. In the particular arrangement illustrated,leads 26, shown in FIGS. 2 and 3, are formed over the first surface 10of the structural layer whereas leads 28 are formed on the downwardlyfacing or bottom surface of the structural layer.

As best seen in FIG. 3, each lead 26 has an enlarged first end 30, anenlarged second end 32 and an elongated section 34 which is narrowerthan the end sections 30 and 32. Following formation of the leads, theassembly is exposed to an etchant such as an oxidizing plasma asdescribed in the aforementioned '750 and '371 applications thedisclosures of which are hereby incorporated by reference herein. Theetchant attacks the adhesive but does not substantially attack thematerial of the leads. The etching process removes adhesive materialfrom layers 12 and 14. As best seen in FIG. 4, the etching processundercuts the lead and begins removing adhesive from beneath the lead,starting at the edges of the lead. The etching process is terminatedbefore all of the adhesive material has been removed from beneath theleads. In particular, an end connector 36 remains beneath second end 32of the lead. As best appreciated with reference to FIGS. 3 and 4, theconnector 36 has an area smaller than the area of the lead second end.As used in this disclosure, the term “area” refers to area in a planeparallel to the adjacent surface of the support layer 10, unlessotherwise indicated.

Depending upon when the etching process is terminated, there may be astrip-like connector 38 extending the beneath the elongated portion 34of each lead. As will be appreciated from inspection of FIG. 3, thestrip-like connector has a smaller area than the elongated region 34 ofthe lead. If the etching process is allowed to proceed further, thestrip-like connector 38 may be removed entirely, whereas the endconnector 36 remains. In a variant of the process, the enlarged section32 at the second end of the lead is omitted and the process iscontrolled so that the strip-like connector 38 is formed and extends toadjacent to the second end of the lead.

A connector 40 also forms adjacent the first end 30 of the lead. Thefirst ends 30 of the leads typically are anchored permanently tostructural layer 10 by conductive structures (not shown) such as viasand the like extending into or through the conductive structure. Theseconductive structures also connect each lead with other conductiveelements. For example, the vias may extend entirely though the supportlayers 10 and may connect leads 26 with leads 28 on the bottom surface.Connectors similar to those associated with leads 26 are formed betweenthe second-surface leads 28 and the structural layer 10 as, for example,connectors 44 formed from portions of adhesive layer 14. The etchingprocess may be controlled so as to affects only the adhesive layers 12and 14; it does not damage the structural layer 10. In certain cases,particularly where the adhesive is thin, the entire adhesive layer maybe removed during the etching process in those areas which are notcovered by the leads. In this case, some portion of the underlying layermay be removed as well. Depending upon the composition of the adhesiveand the underlying layer, the etch rate through the adhesive may begreater than the etch rate through the underlying layer, so that etchingin those areas not covered by the leads slows or stops when the entireadhesive layer is removed.

The structure can be used in much the same manner as the structuresdescribed in the aforementioned '964 Patent and in the '750 and '371applications. Thus, the second ends of the leads may be engaged withfeatures on a microelectronic device and the microelectronic elementsmay be moved away from structural layer 10 so as to bend the second endsof the leads away from the structural layer. During this process, theconnectors at the second ends, such as connectors 36 and 44 break orpeel away from the leads or peel away from the structural layer.

Numerous variations of the processes discussed above can be utilized.For example, the leads may be formed by an additive process whichdeposits the leads on the adhesive without forming a full metal layer.Also, leads may be formed only on one side rather than on both sides ofthe structural layer. Other conductive features may be formed on thestructural layer by similar processes. The particular processesdiscussed above utilize two aspects of the invention in combination: theuse of the adhesive layer to attach the sheet to the frame and formationof releasable leads by etching the adhesive layer. These aspects can beused separately from one another. For example, a support structure maybe attached using an adhesive layer as discussed above and processed toform elements other than leads. Also, etching of an adhesive layer toform releasable attachments for lead ends may be practiced using anadhesive layer on a support structure which is not mounted on a frame orwhich is attached to a frame by means other than those discussed above.The process can be applied to form releasable leads on a standard tapeautomated bonding (“TAB”) type laminate, which typically includes adielectric layer, an adhesive layer and a metal layer laminated to oneanother.

In a further embodiment of the invention, the support structure mayinclude a metallic layer 110 (FIG. 5). The adhesive layer 112 isprovided on a surface of the metallic layer and leads 126 are providedon the exposed surface of the adhesive layer. The leads 126 areconnected by electrically conductive anchors 113 extending through theadhesive layer 112 at the first ends of the leads. Spots of anetch-resistant metal 115 are deposited on the second surface of thestructural layer, opposite from the leads. Adhesive layer 112 is thenetched to form connectors 136 at the second ends of leads 126. Thesecond ends of the leads may be bonded to contacts 127 on amicroelectronic element (FIG. 7). The microelectronic element is thenmoved away from support layer 110. As described in greater detail in PCTInternational Publication WO98/28955 the disclosure which is also herebyincorporated by reference herein and a copy of which is annexed hereto,encapsulant 117 is provided between the structural layer and themicroelectronic component so the encapsulant surrounds the bent leads126′ (FIG. 7). The structural layer 110 (FIGS. 5 and 6) is exposed to anetchant which removes the structural layer except at the spots protectedby etch-resistant metal 115, thereby forming terminals 119 connected tothe leads.

The foregoing processes can be used to fabricate releasable leads andstructures using releasable leads as taught in co-pending, commonlyassigned United States Provisional Patent Applications No. 60/088,519Jun. 8, 1998 and No. 60/087,286, filed May 29, 1998 the disclosures ofwhich are hereby incorporated by reference herein. Certain aspects ofthe invention are further described in the following claims:

What is claimed is:
 1. A connection component for making microelectronicassemblies comprising: (a) a structural layer having a first surface;(b) a plurality of conductive leads each having a first end and a secondend overlying said first surface of said structural layer, the firstends of said leads being permanently connected to said structural layer;and (c) an adhesive disposed between the said second ends of said leadsand said structural layer, said adhesive forming connections betweensaid second end of said leads and said structural layer, saidconnections having areas smaller than the areas of said second ends,said second ends of said leads being releasably attached to saidstructural layer by said connections.
 2. A connection component asclaimed in claim 1 wherein an adhesive extends between said first endsof said leads and said structural layer and forms anchors having areaslarger than the areas of said second ends.
 3. A connection component asclaimed in claim 1 wherein said structural layer includes a dielectriclayer juxtaposed with said adhesive.
 4. A connection component asclaimed in claim 1 further comprising a frame overlying portions of saidstructural layer and an adhesive retaining said structural layer inengagement with said frame, said frame holding said structural layer intension.
 5. A connection component as claimed in claim 1 wherein saidstructural layer includes a metallic layer.
 6. An in-process componentfor making electronic connection components comprising: (a) a framehaving structure defining an aperture; and (b) a sheetlike compositeelement including a structural layer having oppositely-directed firstand second surfaces, and a first adhesive layer overlying said firstsurface of said structural layer, said composite element extendingacross the aperture of said frame, said composite element includingperipheral portions overlying said structure of said frame and a centralportion aligned with said aperture, said adhesive layer extending intosaid peripheral portions and securing said structural layer to saidframe, said adhesive layer also extending into said central portion ofsaid composite element, wherein said structural layer includes adielectric layer, the component further comprising a metallic layeroverlying said central portion of said composite element and secured tosaid structural layer by said adhesive layer.
 7. An in-process componentas claimed in claim 6 further comprising a second adhesive layeroverlying said second surface of said structural layer.
 8. An in-processcomponent as claimed in claim 7 further comprising a second metalliclayer overlying said second adhesive layer.